Jim Grant's Tech Tips
'90 Ford F150 No Heat
have gone through all of the vacuum lines and misc. vacuum motors and
checked for leaks or defects for the heater on my 90 Ford F-150.
I have replaced the heater core and the thermostat. I still cannot get
heat into the cab. What can I do next? Could it be a water flow problem
(not enough water being pumped through the heater core)?.....Jeff
A water/coolant flow problem could easily explain your no heat condition.
When the engine is at operating temperature both the supply and return
heater hose should be hot. As for coolant flow, it should be in the area
of a garden hose. In most cases a garden hose will not flow as much as
the flow through a heater with the engine revved up. If flow is low a
water pump may be needed to correct your heat problem.